1. Field of the Invention
The invention relates to a monitoring system, more particularly to a closed-loop monitoring system.
2. Description of the Related Art
Referring to FIG. 1, a conventional control system is shown to include a host device 11, and a plurality of control devices 13 coupled in series to the host device 11 through a single transmission line 12. The host device 11 is operable to generate encoded audio signals and encoded control signals, and outputs the encoded audio signals and the encoded control signals to the transmission line 12 through an output side 111 thereof. Each control device 13 has an input side 131 coupled to the transmission line 12, and includes: a signal current generating element 132 coupled across the input side 131 such that the encoded audio and control signals pass through the signal current generating element 132; a current inducting device 133 disposed adjacent to the signal current generating element 132 for generating induced signals when the encoded audio and control signals pass through the signal current generating element 132; and a control unit 134 coupled to the current inducting device 133, an electronic device 15, such as a lamp device, and a loudspeaker 14, receiving the induced signals from the current inducting device 133, identifying audio signals and a control signal from the induced signals received thereby, and outputting the audio signals and the control signal to the loudspeaker 14 and the electronic device 15, respectively, such that the audio signals are reproduced by the loudspeaker 14 and that the electronic device 15 is operated based on the control signal.
In such a configuration, distortion of the encoded signals can be minimized, thereby ensuring a stable signal transmission. However, when undesired operation of one electronic device 15 occurs, a user cannot determine whether said one electronic device 15 malfunctions or the transmission line 12 is cut off. As a result, after said one electronic device 15 is checked and determined to be normal, a long period of time is required to find an exact position where the transmission line 12 is cut off.